Abstract: A piston valve diaphragm for a percussion apparatus including a valve portion having a diaphragm bore and a fluid supply source. A piston having a first piston surface and a second piston surface are also included. A diaphragm is mounted in the diaphragm bore and is displaceable in a first direction which permits fluid communication between the fluid supply source and the first piston surface and limits fluid passage between the fluid supply source and the second piston surface. Displacement of the diaphragm in a second direction permits fluid communication between the fluid supply source and the second piston surface and limits fluid passage between the fluid supply and the first piston surface. The diaphragm may be formed entirely from a flexible material or may contain a rigid center portion with flexible edge portion.